Stabilization means for tank mounting

ABSTRACT

A liquefied gas tanker of the kind having at least one storage tank is provided with a stabilizing device comprising a structural key beam extending for and aft above the tank, on which is located, via bearer blocks of insulation material, a first keyway carried by the top of the tank, each end of the key beam being a sliding fit in a second keyway provided on a transverse girder of the tanker. The arrangement thus permits relative movement between the tank and structural beam and between the beam and the hull of the tanker. A similar stabilizing arrangement can be provided transversely of the tanker for stabilizing against pitching movements.

I United States Patent :1 1111 3,830,181 Tornay Aug. 20, 1974 [54] STABILIZATION MEANS FOR TANK 3,583,351 6/1971 Gorman ll4/74 A MOUNTING 3,6l2,333 l0/l97l Cowles ll4/74 A [75] Inventor: Illlldrhund George Tornay, New York, Primary Examiner Trygve Blix Assistant Examiner-Stuart M. Goldstein [73] Assignee: Conch International Methane Limited, Nassau, Bahamas [5 7] ABSTRACT [22] Filed: May 29, 1973 A liquefied gas tanker of the kind having at least one storage tank is provided with a stabilizing device com- [211 App! 364485 prising a structural key beam extending for and aft above the tank, on which is located, via bearer blocks [30] Foreign Application Priority Data of insulation material, a first keyway carried by the June 5, 1972 Great Britain 26129/72 top of the tank, each end Of the y beam being a slit!- ing fit in a second keyway provided on a transverse 52 vs. C: 114/74 A, 220/9 LG girder ef the tanker- The arrangement thus permits 51 1111. c: B63b 25/08 relative movement between the tank and sttuetutel [58] Field of Search 114/74 A; 220/9 LG, 15 beam and between the beam and the of the tanker. A similar stabilizing arrangement can be pro- [56] References Cited vided transversely of the tanker for stabilizing against UNITED STATES PATENTS Pwhmg mvemems- 3,072,088 l/l963 Stroschein 114/74 A 10 Claims, 4 Drawing Figures IOa II a" l p 2 I4 "0.

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PAIENIEDmczomm saw u or 4 STABILIZATION MEANS FOR TANK MOUNTING This invention relates to tankers for the storage and transportation of liquid having a temperature differing widely from ambient temperature and it relates more particularly to the over-water transportation of low boiling point liquefied gas, such as liquefied natural gas.

The invention will be described with reference to the storage of large volumes of gas in a liquefied state in storage tanks of a marine tanker for over-water transporation of natural gas from a source of plentiful supply to an area where a deficiency exists. It will be understood that the concepts of this invention will have application also to marine tankers for the storage and transportation of other low boiling liquefied gases or liquids maintained at an extremely low temperature and that the concepts of this invention are applicable also to other means of transportation in which the storage tanks might be subject to pitching or rolling movements, in addition to expansion and contractions due to temperature change.

Each storage tank is exposed to extremely wide temperature change in use which, in the storage and transportation of liquefied natural gas, may range from about plus 38C during installation or when the tank is empty, to a temperature of about l6lC when the tank is filled with liquid cargo. When, as in the usual practice, the tanks are fabricated of a metal which is relatively insensitive to the temperature change, such as aluminum or alloys of alluminum, stainless or or the like high nickel steels, copper, brass, etc., a rather wide change in dimension of the tank will take place by reasons of expansions and contractions due to temperature change. In an aluminum storage tank with a length of 30 metres, a change of 8 or more centimeters in any direction can occur. As a result, the tanks cannot be rigidly tied into a tanker structure which is not equally subjected to the same change in dimension. Instead, it becomes necessary to support the tank within the thermally insulated space in a manner which will enable the tank freely to expand and contract relative to the tanker structure. On the other hand, it is undesirable to allow the tank to move from a stabilized position, for example, in response to the pitching and rolling movements of the tanker, otherwise uncontrolled forces will be developed which might lead to the development of undesirable and dangerous conditions.

It is an object of this invention to provide a means for top stabilization of a storage tank of large capacity without rigid attachment to the supporting structure thereby permitting relative movement between the tank and its supporting structure in response to expansion and contraction forces but without movement of the tank with reference to-its stabilized position.

According to this invention in a tanker for the storage and transportation of liquid having a temperature differing widely from ambient temperature, said tanker having at least one storage tank and stabilizing means for the top of said tank, said stabilizing means comprises a first keyway rigid with the tank and extending horizontally in a fore and aft direction above the top wall of the tank, a key in the form of a structural beam, and bearer blocks of a thermally insulating material having substantial compressive strength between the co-operating keying faces of said first keyway and said key, each end of said beam being a sliding fit within a second keyway provided on a transverse girder of the tanker.

It will be appreciated that in a marine tanker with such an arrangement, not only is the top of the tank stabilized against movement transversely of the tanker, but differential thermal movement between the tank and the deck structure in the fore and aft direction is accommodated by the first keyway, while differential movement between the key and the deck structure, due to hull deflections, is accommodated by the second keyway.

In order that the invention will be readily understood and further features made apparent, one embodiment of the invention applied to a marine tanker for overwater transportation of liquefied gas will now be described by way of example to the accompanying drawings, in which:

FIG. 1 is a fragmentary plan view of the central portion of a storage tank top wall in position beneath the tanker deck support structure;

FIG. 2 is a schematic side view of the tanker partly in broken-away section and partly on the line IIII of FIG. 1, showing the general relationship of the elements;

FIG. 3 is a schematic view on the line IIIIII of FIG. 1; and

FIG. 4 is an enlarged fragmentary plan view of a fixing detail.

The storage tank shown in FIG. 1 is preferably of prismatic form with a fiat top wall 1, for example, as described in the specification of U.S. Pat. No. 3,062,397 to H. W. Bergmann, filed Mar. 16, 1961. Also, as described in said patent specification and shown in FIG. 1, the top wall 1 of the tank is provided centrally thereof with a dome 2 adapted to extend through a suitable aperture in the deck structure of the tanker so as to serve as an access for the cargo inlet and outlet pipes, schematically indicated at 2a in FIG. 2. Again, as described in said patent specification, the tanker would have several such storage tanks fitted therein, preferably with each tank located in an insulated hold defined by cofferdams extending transversely of the tanker hull. In this embodiment the storage tank is fitted with an internal bulkhead extending along the line 3 which is the fore and aft center-line of the tanker (reference A-A in FIG. 1) dividing the tank into two compartments, and a transverse internal swash bulkhead along the line A, although these are not a part of the invention and the tank may have any other form of internal reinforcement or construction.-

FIG. 2 shows a typical mid-section of the ship 10 containing the tank 1,-which is supported on the bottom of the ship in any known or conventional manner, schematically indicated by insulating blocks 100, the arrangement conventionally being such as to provide for thermal expansion and contraction of the bottom of the tank relative to the hull of the vessel. The present invention is concerned only with the top support of the tank.

The deck 10a of the tanker is provided with a lattice of girders 11 and 12 (FIGS. 1 and 2) which may conveniently support the deck, and which are a part of the rigid framework of the vessel. The top of tank 1 is slidably restrained by girders 11 and 12 as will be explained in detail below. The customary tank trunk 2 extends through an opening in the deck and is provided with suitable inlet and outlet pipes 2a, for filling and emptying the tank of its contents.

Referring also to FIGS. 2 and 3, in accordance with the invention, the top wall 1 of the tank has a number of aligned and spaced first keyways 5 which, when the storage tank is in position within its hold space, extend horizontally substantially along the fore and aft centerline AA of the tanker. Said keyways are in two sets providing a line of keyways on each side of the tank dome 2. Each first keyway 5 is of the same material as the tank, i.e., a material such as aluminum or 9% nickel steel which remains ductile at the temperature of the liquefied gas, and is supported above the level of the top wall 1 of the tank by webs 5a fixed to said top wall. The side faces of the keyways 5 are lined with blocks 6 of thermally insulating material having substantial compressive strength, e.g., materials sold in Great Britain under the trade names PERMALI (Reg. Trade Mark) or PANELYTE (Reg. Trade Mark) are suitable, but any other suitable material may also be employed. The inner faces of the blocks 6 of each keyway are adapted to fit closely against the sides of a a cooperating key 7 in the form of a structural beam, said beam being generally of channel shape with intermediate transverse stiffening webs 8. The positioning of the keyways 5 on the storage tank is such that, when fitted into its hold space, each keyway lies substantially centrally beneath a lattice opening 9 defined by transverse and longitudinal girders 11, 12 respectively of the frame structure for the deck of the tanker. The length of each co-operating key 7 is such that, when fitted, it lies within the webs 11a (see FIG. 2) of the respective transverse girders 11, while being supported on the flanges 11b of said girders (see FIG. 4).

Referring now particularly to FIG. 4, each end of each key beam 7 has a rectangular plate 13 welded thereto and the vertical edges of each plate are adapted to fit closely within a pair of shear blocks 14 welded to the web 11a of the respective girder 11, thus providing a second key and keyway arrangement. The web 11a of each girder 11 is thickened as shown at 110 to accommodate shear loads transmitted thereto by the shear blocks 14.

In use, the top key arrangement described has the advantage that thermal movement of the top of the storage tank with respect to the deck structure in vertical plane extendingin the fore and aft direction of the tanker is accommodated by the first keyway 5, while differential movement between the key beam 7 and said deck structure due to hull deflection is accommodated by the second keyway. Furthermore, the loads transmitted by the key beam 7 to the deck structure via the shear blocks 14 are in the form of point loads without bending moments, with the result that the top key arrangement described minimizes the possibility of complex stresses being induced at the junction of the key beams 7 and the girders 11 as would be the case if the key beams 7 were welded to said girders.

Other advantages are as follows i. By leaving the welding operation of the ends of the key beams 7 to their end plates 13 as the final fitting operation some tolerance is provided for in both the fore and aft, and particularly the transverse location of each storage tank in its hold space.

A further keying arrangement similar to that described above may be provided between the tank top wall and the longitudinal girders 12 of the deck structure, as shown generally referenced at 15 in FIG. 1, said further keying arrangement being orthogonal to that described above and serving to key said tanks against pitching movement of the tanker at sea. The angular motions associated with such movement are small compared with those associated with rolling movement and normally one keying arrangement 15 on each side of the tank dome 2 would be sufficient to retain the storage tank against pitching.

Since ship building and the construction of cryogenic tanks are operations which often can best be performed by specialists at two different locations, it has been proposed to construct the tanks of a marine tanker away from the ship yard and float them to the latter when finished, after which they can be lowered into position in ii. Following from the above all the fitting compo- 6 nents, including the insulating blocks 6 may be prefabricated to finished dimensions.

the tankers hull. Alternatively, if the tank construction site is a substantial distance from the ship yard, the tanker may be partly completed with the deck temporarily fitted, and the tanker may then sail to the tank construction site, where the deck is removed, the tanks fitted and the deck refitted for return to the ship yard for final completion. In either construction method, the top key and keyway arrangement described above is particularly suitable, since this arrangement may be readily fitted once the deck is located in position, either as a temporary or as a permanent measure.

It will be understood that the key and keyway are interchangeable, i.e., the key may equally well be carried by the tank and the keyway by the tanker, as this does alter the essential co-operation between them.

I claim:

1. A marine tanker for the storage and transportation of liquid having a temperature differing widely from ambient temperature, said tanker housing at least one storage tank and having stabilizing means for the top of said tank, wherein said stabilizing means comprises:

a. a first keyway fixed to the top of said tank and extending horizontally in a longitudinal direction above the top wall of the tank,

b. a key in the form of a beam carried by the tanker above and adjacent to the tank and extending downwardly into said keyway, the ends of said beam extending out beyond said keyway,

c. bearer blocks of thermally insulating material having substantial compressive strength fixed between the co-operating keying faces of said keyway and said key so as to permit relative sliding motion between them,

d. a pair of spaced transverse girders carried by the tanker transverse to the keyway and respectively adjacent the ends of the keyway,

e. each of said transverse girders carrying a second keyway embracing the respective ends of said key with a sliding fit so as to permit relative vertical and longitudinal motion between said beam and said second keyways while restraining relative trans verse motion of said members.

2. A tanker for the storage and transportation of liquid having a temperature differing widely from ambient temperature, said tanker housing at least one storage tank and having stabilizing means for the top of said tank, wherein said stabilizing means comprises:

a. a first keyway rigid with the tank and extending horizontally in a longitudinal direction above the top wall of the tank,

b. a key, in the form of a structural beam, carried by the tanker above and adjacent to the tank,

c. bearer blocks of a thermally insulating material having substantial compressive strength fixed between the co-operating keying faces of said first keyway and said key,

d. second keyways provided in a pair of spaced transverse girders carried by the tanker,

e. each end of said beam being located in one of said second keyways with a sliding fit, to permit relative vertical and longitudinal sliding motion between said beam and said second keyways while restraining relative transverse motion between them.

3. A tanker according to claim 2, wherein the storage tank is located beneath a number of spaced transverse girders, and a number of aligned keys are provided one between each pair of adjacent girders.

4. A tanker according to claim 3, wherein each key has a co-operating first keyway on the tank, and the keyways are aligned and spaced to correspond with the spacing of the keys.

5. A tanker according to claim 4, wherein the tank extends substantially over the width of the tanker, and

the keys and keyways are arranged along the fore and aft center-line of the tanker.

6. A tanker according to claim 2, wherein a further said key and said first and second keyway arrangement is provided between the tank and longitudinal girders of the tanker.

7. A tanker according to claim 2, wherein each said first keyway is of the same material as the tank and is supported above the tank top wall by webs extending from the latter.

8. A tanker according to claim 2, wherein the tanker is a marine tanker for over-water transportation of said liquid and said girders form part of the tanker deckstructure.

9. A tanker according to claim 2, wherein each key is in the fonn of a channel section beam with a-plate at each end thereof, each plate having two parallel edges arranged vertically for sliding movement within a pair of spaced shear blocks, constituting said second keyway, attached to the respective girder.

10. A tanker according to claim 9, wherein the webs of said girders are thickened in the area of the shear blocks for accommodating shear loads transmitted by said shear blocks. 

1. A marine tanker for the storage and transportation of liquid having a temperature differing widely from ambient temperature, said tanker housing at least one storage tank and having stabilizing means for the top of said tank, wherein said stabilizing means comprises: a. a first keyway fixed to the top of said tank and extending horizontally in a longitudinal direction above the top wall of the tank, b. a key in the form of a beam carried by the tanker above and adjacent to the tank and extending downwardly into said keyway, the ends of said beam extending out beyond said keyway, c. bearer blocks of thermally insulating material having substantial compressive strength fixed between the co-operating keying faces of said keyway and said key so as to permit relative sliding motion between them, d. a pair of spaced transverse girders carried by the tanker transverse to the keyway and respectively adjacent the ends of the keyway, e. each of said transverse girders carrying a second keyway embracing the respective ends of said key with a sliding fit so as to permit relative vertical and longitudinal motion between said beam and said second keyways while restraining relative transverse motion of said members.
 2. A tanker for the storage and transportation of liquid having a temperature differing widely from ambient temperature, said tanker housing at least one storage tank and having stabilizing means for the top of said tank, wherein said stabilizing means comprises: a. a first keyway rigid with the tank and extending horizontally in a longitudinal direction above the top wall of the tank, b. a key, in the form of a structural beam, carried by the tanker above and adjacent to the tank, c. bearer blocks of a thermally insulating material having substantial compressive strength fixed between the co-operating keying faces of said first keyway and said key, d. second keyways provided in a pair of spaced transverse girders carried by the tanker, e. each end of said beam being located in one of said second keyways with a sliding fit, to permit relative vertical and longitudinal sliding motion between said beam and said second keyways while restraining relative transverse motion between them.
 3. A tanker according to claim 2, wherein the storage tank is located beneath a number of spaced transverse girders, and a number of aligned keys are provided one between each pair of adjacent girders.
 4. A tanker according to claim 3, wherein each key has a co-operating first keyway on the tank, and the keyways are aligned and spaced to correspond with the spacing of the keys.
 5. A tanker according to claim 4, wherein the tank extends substantially over the width of the tanker, and the keys and keyways are arranged along the fore and aft center-line of the tanker.
 6. A tanker according to claim 2, wherein a further said key and said first and second keyway arrangement is provided between the tank and longitudinal girders of the tanker.
 7. A tanker according to claim 2, wherein each said first keyway is of the same material as the tank and is supported above the tank top wall by webs extending from the latter.
 8. A tanker according to claim 2, wherein the tanker is a marine tanker for over-water transportation of said liquid and said girders form part of the tanker deck-structure.
 9. A tanker according to claim 2, wherein each key is in the form of a channel section beam with a plate at each end thereof, each plate having two parallel edges arranged vertically for sliding movement within a pair of spaced shear blocks, constituting said second keyway, attached to the respective girder.
 10. A tanker according to claim 9, wherein the webs of said girders are thickened in the area of the shear blocks for accommodating shear loads transmitted by said shear blocks. 